What you think is better? For games for sure.
1. A demoversion
Give away 1/3 of your game and let the people order the full version.
2. Traditional Shareware
Give away your complete game and let people register (pay).
3. Stephen Kings Method (dunno if it already has another name)
Give away 1/3 of your game and wait for people to register (pay) before you release the second part and after the same procedure the third part.

my gut reaction would be to just do a demo, like most big companies do. However I think the stephen king idea is a good one. I would be more likely to buy a game like Shogun if it was half the price, for example, and havign bought it, i would be happy to buy extra features (different clans for example) for a few dollars each, and I hate to think how much i would spend on Age Of Empires II if you had to buy the different scenarios instead of getting them free.The problem of course, is that this means keeping the level editor out of the public domain, which could actually have an adverse effect on sales. Still, it bugs we that the SimCity3000 developers (crap game) have earned as much out of me as the Age Of Empires 2 guys (awesome game).